wallet/src/ristretto255.cpp

#include "stdafx.h"
void randombytes_buf(std::span<byte> in) { randombytes_buf(&in[0], in.size_bytes()); }
void randombytes_buf(std::span<   char> in) { randombytes_buf(&in[0], in.size_bytes()); }
namespace ristretto255 {
	bool scalar::constant_time_required{ true };
	bool point::constant_time_required{ true };

	point point::operator*(const scalar &sclr) const& noexcept {
		point me;
		auto i{ crypto_scalarmult_ristretto255(&me.blob[0], &sclr.blob[0], &blob[0]) };
		assert(i == 0);
		return me;
		}

	point point::operator*(int i)  const& noexcept {
		return scalar(i) * (*this);
	}

	point point::ptZero({
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00});
	point point::ptBase({
		0xe2, 0xf2, 0xae, 0x0a, 0x6a, 0xbc, 0x4e, 0x71, 0xa8, 0x84, 0xa9, 0x61, 0xc5, 0x00, 0x51, 0x5f, 0x58, 0xe3, 0x0b, 0x6a, 0xa5, 0x82, 0xdd, 0x8d, 0xb6, 0xa6, 0x59, 0x45, 0xe0, 0x8d, 0x2d, 0x76});

	static const scalar curveOrder({ 0xed, 0xd3, 0xf5, 0x5c, 0x1a, 0x63, 0x12, 0x58, 0xd6, 0x9c, 0xf7,
		0xa2, 0xde, 0xf9, 0xde, 0x14, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10 });
	const scalar& scalar::scOrder{ curveOrder };

	std::strong_ordering scalar::operator<=>(const scalar& sclr) const& noexcept {
		static_assert(std::endian::native == std::endian::little);
//		Instead of a static assert, we really should have an if constexpr()
//		that defines reverse iterators for little endian order
//		and defines forward iterators for big endian order.
//		but we will fix that when the time comes.
//		as it depends on how the libsodium library will implement
//		scalars on big endian order.
		std::strong_ordering retval{ std::strong_ordering::equal };
		constexpr auto bg = sizeof(scalar::blob);
		typedef const std::array<uint64_t, sizeof(scalar::blob)/sizeof(uint64_t) >as_uint64_t;
		auto lh{ reinterpret_cast<as_uint64_t&>(this->blob)};
		auto rh{ reinterpret_cast<as_uint64_t&>(sclr.blob) };
		static_assert(sizeof(as_uint64_t) == sizeof(sclr.blob));
		auto p{ lh.end() };
		auto q{ rh.end() };
		do
		{
			auto vp{ *--p };
			auto vq{ *--q };
			retval = vp <=> vq;
		}
		while (std::is_eq(retval) &&
			bool(p > lh.begin()));
		return retval;
	}

	signed_text::signed_text(
		const scalar &k,		//	Signer's secret key
		const point &Kin,			//	Signer's public key
		std::span<char> txtin	//	Text to be signed.
	)
	: txt(txtin), K(Kin)
	{
		assert(k.valid());
		assert(K.valid());

		/*	• Compute r = H(k|M), a per message private key.  Or r can be an unpredictable secret scalar.
			• Compute R = r*B, a per message public key<br/>
			• Compute c = H(R|M).<br/>
			• Compute s = r+c*k. (Note that sB = r*B+c*k*B = R+c*K.)*/
		scalar r(hash<512>(k, txtin));
		point R(r.timesBase());
		c = scalar (hash<512>(R, txtin));
		s = r + c * k;
	}

	bool signed_text::verify() {
		/*	• Check that c, s are valid scalars
			• Check that K, the signing public key, is a valid member of the prime order group
			• Compute R = sB − cK
			• Check that c = H(R | M) */
		if (!c.valid() || !s.valid() || !K.valid())return false;
		else {
			point R = s.timesBase() - c * K;
			return c==scalar(hash<512>(R, txt));
		}
	}

} //end ristretto255 namespace
using ristretto255::scalar, ro::CompileSizedString, ro::bin2hex, ro::to_base64_string;

auto reverse_byte_order(std::array < uint8_t, sizeof(scalar)>const& ac) {
	std::array <uint8_t, sizeof(scalar)> ar;
	auto p = ar.rbegin();
	for (auto x : ac) {
		*p++ = x;
	}
	return ar;
}

template<> CompileSizedString < 2 * sizeof(scalar)>
	bin2hex<scalar>(const scalar& sc) {
	CompileSizedString <2 * sizeof(scalar)>sz;
	auto bigendian = reverse_byte_order(sc.blob);
	sodium_bin2hex(&sz[0], sizeof(sc.blob) * 2 + 1, &bigendian[0], bigendian.size());
	return sz;
}

template<> scalar ro::hex2bin<scalar>(const CompileSizedString< (2 * sizeof(scalar))>& sz) {
	scalar sc;
	sc.blob = reverse_byte_order(ro::hex2bin<decltype(sc.blob)>(sz));
	return sc;
	}

template<> CompileSizedString < (sizeof(scalar) * 8 + 5) / 6>
	to_base64_string<scalar>(const scalar& sc) {
	CompileSizedString < (sizeof(sc.blob) * 8 + 4) / 6> sz;
	auto bigendian = reverse_byte_order(sc.blob);
	bits2base64(
		&(bigendian[0]), 4, sizeof(bigendian)*8-4,
		std::span<char>(sz)
	);
	return sz;
}